In the cutting of spiral bevel or hypoid gears, if the direction of cutter rotation is selected such as to produce the cutting action commonly known as climb milling, the torque load imposed on the work and work spindle by each individual cutting blade is in the direction of the work rotation. This means that as each cutter blade enters the cut, it tends to drive the work spindle rotation momentarily ahead relative to the generating gear train which normally rotates the spindle in timed "generating" relation to the rotation of the cutter-supporting cradle. This condition tends to cause a repetitive winding and unwinding in the generating train such as to take up backlash through the train first in one direction, then the other. This causes rattle and vibration in the drive which is transmitted to the work spindle. The result is unevenness in the cut, poor finish and cutter life, and even cutter breakage or machine damage can result.
In the past, it has been customary to apply a constant brake load to the work spindle, in an attempt to maintain sufficient torque load on the spindle at all times so as to keep the generating train backlash always taken up in the normal driving direction. But work spindle brakes are subject to uneven action and wear, requiring frequent readjustment and they can be a continuing maintenance problem. The inconsistency and maintenance of such brakes are particularly troublesome in roughing operations where heavy cutter loads and corresponding heavy brake loads are involved.